Flameless combustion heater

ABSTRACT

A flameless combustion heater is described, that comprises an oxidation conduit and a fuel conduit positioned within the oxidation conduit to form an oxidation zone having an inlet and an outlet, said fuel conduit having a plurality of openings that provide fluid communication from within the fuel conduit to the oxidation conduit wherein the longitudinal axis of at least one opening forms an oblique angle with the inner surface of the oxidation conduit. A method for providing heat to a process conduit is described, that comprises providing an oxidation conduit; providing a fuel conduit having a plurality of openings that provide fluid communication from within the fuel conduit to the oxidation conduit wherein the longitudinal axis of at least one opening forms an oblique angle with the inner surface of the oxidation conduit; providing a process conduit in a heat exchange relationship with the oxidation conduit; introducing fuel into the fuel conduit; introducing an oxidant into the oxidation conduit; and introducing the fuel into the oxidation conduit through the plurality of openings such that flameless combustion occurs in the oxidation conduit.

This application claims the benefit of U.S. Provisional Application No. 60/950,938, filed Jul. 20, 2007 which is hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to a flameless combustion heater and a method for providing heat to a process.

BACKGROUND OF THE INVENTION

Flameless combustion heaters are described in U.S. Pat. No. 7,025,940. The patent describes a process heater utilizing flameless combustion, which is accomplished by preheating a fuel and combustion air to a temperature above the auto-ignition temperature of the mixture. The fuel is introduced in relatively small increments over time through a plurality of orifices in a fuel gas conduit, which provide communication between the fuel gas conduit and an oxidation reaction chamber. As described in the patent, a process chamber is in heat exchange relationship with the oxidation reaction chamber.

Flameless combustion heaters can encounter problems related to the fuel conduit and the openings that provide for communication from within the fuel gas conduit to the oxidation reaction chamber. Conventional flameless combustion heaters have openings that have a longitudinal axis perpendicular to the inner surface of the oxidation conduit.

The fuel passing through these perpendicular openings has a tendency to impinge directly on the inner surface of the oxidation conduit. Thus, a minimum distance is typically maintained between the outside of the fuel conduit and the inside of the oxidation conduit to reduce hot spots on the oxidation conduit wall. The oxidant flow may be increased to address this tendency to impinge, but that results in disadvantages such as excessive pressure drop. Further, the fuel exiting the perpendicular openings may not mix well with the oxidant. This incomplete mixing may occur immediately downstream of the opening.

The heat provided by the flameless combustion is to a certain extent typically concentrated in the same radial orientation and directly downstream of the opening. This can result in uneven heating of the heater materials of construction that leads to thermal expansion that tends to bend the fuel and oxidation conduits. Additionally, this results in uneven heating of the material to be heated by the heater.

SUMMARY OF THE INVENTION

The invention provides a flameless combustion heater comprising an oxidation conduit and a fuel conduit having a plurality of openings that provide fluid communication from within the fuel conduit to the oxidation conduit wherein the longitudinal axis of at least one opening forms an oblique angle with the inner surface of the oxidation conduit.

The invention further provides a method for providing heat to a process conduit comprising: providing an oxidation conduit; providing a fuel conduit having a plurality of openings that provide fluid communication from within the fuel conduit to the oxidation conduit wherein the longitudinal axis of at least one opening forms an oblique angle with the inner surface of the oxidation conduit; providing a process conduit in a heat exchange relationship with the oxidation conduit; introducing fuel into the fuel conduit; introducing an oxidant into the oxidation conduit; and introducing the fuel into the oxidation conduit through the plurality of openings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a two-tube flameless combustion heater with acute angled openings.

FIG. 1 a depicts a cross-sectional view of the heater of FIG. 1.

FIG. 1 b depicts a cross-sectional view of the heater of FIG. 1.

FIG. 2 depicts a three-tube flameless combustion heater with acute angled openings.

FIG. 2 a depicts a cross-sectional view of the heater of FIG. 2.

FIG. 3 depicts a four-tube flameless combustion heater with acute angled openings.

FIG. 3 a depicts a cross-sectional view of the heater of FIG. 3.

FIG. 4 depicts a two-tube flameless combustion heater with obtuse angled openings.

FIG. 4 a depicts a cross-sectional view of the heater of FIG. 4.

FIG. 4 b depicts a cross-sectional view of the heater of FIG. 4.

FIG. 5 depicts a three-tube flameless combustion heater with obtuse angled openings.

FIG. 5 a depicts a cross-sectional view of the heater of FIG. 5.

FIG. 6 depicts a four-tube flameless combustion heater with obtuse angled openings.

FIG. 6 a depicts a cross-sectional view of the heater of FIG. 6.

FIG. 7 depicts a two-tube flameless combustion heater with tangential openings.

FIG. 7 a depicts a cross-sectional view of the heater of FIG. 7.

FIG. 8 depicts a three-tube flameless combustion heater with tangential openings.

FIG. 8 a depicts a cross-sectional view of the heater of FIG. 8.

FIG. 9 depicts a four-tube flameless combustion heater with tangential openings.

FIG. 9 a depicts a cross-sectional view of the heater of FIG. 9.

FIG. 10 depicts an embodiment that uses a flameless combustion heater in an ethylbenzene dehydrogenation process.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a flameless combustion heater that is used in the direct transfer of heat energy released by the flameless combustion of fuel. The heater has many possible uses and applications including heating underground formations and heating process streams. The flameless combustion heater is especially useful in conjunction with processes that carry out endothermic reactions, for example, dehydrogenation of alkylaromatic compounds and steam methane reforming. The invention provides a flameless combustion heater with at least one opening in the fuel conduit that forms an oblique angle with the inner surface of the oxidation conduit. Angled openings reduce the problems associated with fuel impingement on the inner surface of the oxidation conduit and improve the mixing of fuel and oxidant in the oxidation conduit.

Flameless combustion in a heater can be accomplished by preheating an oxidant stream and a fuel stream sufficiently that when the two streams are combined the temperature of the mixture exceeds the auto-ignition temperature of the mixture, but the temperature of the mixture is less than a temperature that would result in the oxidation upon mixing being limited by the rate of mixing as described in U.S. Pat. No. 7,025,940 which is herein incorporated by reference. The auto ignition temperature of the mixture depends on the types of fuel and oxidant and the fuel/oxidant ratio. The auto ignition temperature of mixtures used in a flameless combustion heater may be in a range of from 850° C. to 1400° C. The auto ignition temperature may be reduced if an oxidation catalyst is employed in the heater because this type of catalyst effectively lowers the auto-ignition temperature of the mixture.

The fuel conduit provides for the controlled rate of fuel introduction into an oxidation conduit in a manner so as to provide for a desired heat release. The heat release is determined in part by the location and number of openings, which can be tailored to each heater application. The heat release may be constant over the length of the heater, or it may be decreasing or increasing over the length of the heater.

Because there is no visible flame associated with flameless combustion of a fuel, the flameless combustion reaction occurs at a lower temperature than that observed in conventional fired heaters. Due to the lower temperatures observed, and the efficiency of direct heating, the heater may be designed using lower cost materials resulting in reduced capital expenditure.

The flameless combustion heater has two main elements: an oxidation conduit and a fuel conduit. The oxidation conduit may be a tube or pipe that has an inlet for oxidant, an outlet for oxidation products and a flow path between the inlet and outlet. Suitable oxidants include air, oxygen, and nitrous oxide. The oxidant that is introduced into the oxidation conduit may be preheated such that when mixed with fuel, the mixture is at a temperature above the auto-ignition temperature of the mixture. The oxidant may be heated externally to the flameless combustion heater.

Alternatively, the oxidant may be heated inside the heater by heat exchange with any of the streams inside the heater. The oxidation conduit may have an internal diameter of from about 2 cm to about 20 cm. The oxidant conduit may however be larger or smaller than this range depending on the heater requirements.

The fuel conduit transports fuel into the heater and introduces it into the oxidation conduit. The fuel conduit may be a tube or pipe that has an inlet for fuel and a plurality of openings that provide fluid communication from within the fuel conduit to the oxidation conduit. The fuel conduit may be located within and surrounded by the oxidation conduit. The fuel passes through the openings and into the oxidation conduit where it mixes with the oxidant and results in flameless combustion. The fuel conduit may have an internal diameter of from about 1 cm to about 10 cm, preferably from about 1.5 cm to 5 cm. Depending on the design, however, the fuel conduit may have a diameter greater than 10 cm or less than 1 cm.

The geometry, orientation and location of the openings in the fuel conduit may be designed to overcome problems that arise due to the fluid and mixing dynamics of the heater system. The openings can be drilled or cut into the wall of the fuel conduit. The wall of the fuel conduit typically has a thickness of from about 0.25 cm to about 2.5 cm. The openings may have cross sections that are circular, elliptical, rectangular, of another shape, or even irregularly shaped. The openings preferably have a circular cross-section.

The openings may have a cross-sectional area of from about 0.001 cm² to about 2 cm², preferably from about 0.03 cm² to about 0.2 cm². The size of the openings is determined by the desired rate of fuel introduction into the oxidation conduit, but openings that are too small may result in plugging. The openings may be located along the fuel conduit at a distance of from 1 cm to 100 cm in the axial direction from any other opening. The openings are preferably spaced from 15 cm to 50 cm apart in the axial direction. The openings may be positioned in their respective radial planes at different orientations along the length of the fuel conduit. For example, the position of the openings may alternate 180 degrees in the radial plane along the length of the fuel conduit, or they may alternate 120 degrees or 90 degrees. Therefore the position of the openings in the fuel conduit may be such that their orientation in the radial plane alternates along the length of the fuel conduit with their orientations separated by 30 degrees to 180 degrees. It is preferred for the radial orientation of the openings to alternate at from 60 degrees to 120 degrees along the length of the fuel conduit.

In one embodiment, a sintered plate may be used in addition to openings to provide fluid communication from the fuel conduit to the oxidation zone, and the openings in a sintered plate may have a diameter on the order of 10-100 microns.

Different openings along the length of the heater typically have the same cross-sectional area. In the alternative, the cross-sectional area of the openings may be different to provide a desired heat release. Additionally the spacing between openings along the fuel conduit may be different to provide a desired heat release. The openings are typically the same shape. In the alternative, the openings may be different shapes.

The openings each have a longitudinal axis defined by the line that connects the centers of the cross-sections at each end of the opening. The fuel conduit also has a longitudinal axis defined by the line connecting the centers of the cross sections of the conduit.

The term acute angle as used herein is defined as an angle between 0 and 90 degrees. The term obtuse angle as used herein is defined as an angle between 90 and 180 degrees. The term oblique angle as used herein is defined as an angle that is either acute or obtuse.

The flameless combustion heater may additionally comprise a process conduit that carries a process fluid where the process conduit is in heat exchange relationship with the oxidation conduit. The inclusion of a process conduit in the heater allows for direct heating of a process stream. The process conduit may optionally be used to carry out a chemical reaction. The process conduit may contain catalyst to facilitate the chemical reaction. This heater is especially useful for carrying out endothermic reactions because heat is added directly to the process during the reaction. For example, this heater may be incorporated into the dehydrogenation reactor to directly heat the dehydrogenation reaction of ethylbenzene to styrene.

The flameless combustion heater may optionally comprise an oxidant conduit. The oxidant conduit has an inlet for oxidant and an outlet for preheated oxidant that is in fluid communication with the inlet of the oxidation conduit. The oxidant conduit is in a heat exchange relationship with the oxidation conduit and/or the process conduit, which provide direct heat to preheat the oxidant to a temperature sufficient that when mixed with fuel in the oxidation conduit the mixture is at or above the auto ignition temperature.

A preheater may be used to preheat the oxidant before it enters the heater. A preheater may be any apparatus or method that provides heat. The preheater may for example be a conventional heat exchanger or a flameless combustion heater.

Preferred embodiments of the flameless combustion heater will be described further in relation to the Figures presented in this application.

FIGS. 1-3 depict embodiments of flameless combustion heaters with what is hereinafter referred to as acute angled openings. FIG. 1 depicts a flameless combustion heater (10) that has a fuel zone (11) formed by fuel conduit (12) and an oxidation zone (13) formed by oxidation conduit (14). This type of heater is referred to as a two-tube heater. In this embodiment, the fuel conduit (12) is a cylindrical pipe that has an inlet (24) for fuel and a plurality of openings (20). The longitudinal axes (22) of the openings form acute angles (34) with the inner surface of the oxidation conduit (14). Oxidation conduit (14) is a cylindrical pipe concentrically positioned around fuel conduit (12) that has an inlet (26) for preheated oxidant and an outlet (30) for combustion products. In the alternative the oxidant may be introduced at (30) and the combustion products may exit the heater at (26), which provides for a countercurrent flow of the fuel and oxidant. Countercurrent flows of fuel and oxidant can provide better mixing of the fuel and oxidant than co-current flows. The direction of the flows may be changed to suit the desired mixing and heat release of the specific heater application. During operation, the fuel enters fuel zone (11) via inlet (24) and then is mixed with preheated oxidant in oxidation zone (13) after it passes through the angled openings (20). The openings (20) are angled in the direction opposite fuel inlet (24).

The openings are such that the longitudinal axis of an opening forms an angle of less than ninety degrees with the inner surface of the oxidation conduit as measured from the fuel inlet (24) of the fuel conduit (12). These openings are hereinafter referred to as acute angled openings. The longitudinal axis of an opening preferably forms an angle of from twenty to eighty degrees with the inner surface of the oxidation conduit, more preferably from thirty to seventy-five degrees and most preferably from fifty to seventy degrees.

FIG. 1 a is a cross-sectional view of FIG. 1 taken along line A-A. This figure depicts one embodiment where the longitudinal axis of an opening intersects the longitudinal axis of the fuel conduit.

FIG. 1 b is a cross-sectional view of FIG. 1 taken along line B-B. This figure depicts another embodiment where the longitudinal axis of an opening is at a distance (40) from the longitudinal axis of the fuel conduit such that the axes do not intersect. These openings are hereinafter referred to as acute angled tangential openings.

A heater may have a cross-sectional view as depicted in FIG. 1 a (acute angled openings) or a cross-sectional view as depicted in FIG. 1 b (acute angled tangential openings). In the alternative, a heater may have a combination of acute angled openings and acute angled tangential openings and the cross-sectional views of FIG. 1 a and FIG. 1 b would represent the cross-sectional view of the same heater at different points in the heater.

An acute angled opening is angled such that the fuel exiting the opening is directed in the direction opposite the fuel conduit inlet. Acute angled openings result in lower peak temperatures, which reduces the risk to heater materials and allows less expensive materials to be used in heater construction. Further, acute angled openings allow the distance between the fuel conduit and the oxidation conduit to be reduced resulting in a smaller heater and reduced capital expenditure.

Acute angled tangential openings provide for more even heat release in the radial direction. The use of acute angled tangential openings also provides a more even heating profile and improved mixing of the fuel and oxidant. The use of acute angled tangential openings also allows the flameless combustion heater to be operated at a higher fuel/air ratio than a flameless combustion heater with typical perpendicular openings. When less air is needed, the oxidation conduit can be smaller, thus reducing the capital expenditure.

FIG. 2 depicts a flameless combustion heater (10) that has a fuel conduit (12), an oxidation conduit (14), and a process conduit (16). This type of heater is referred to as a three-tube heater and may be used for direct heating of a process fluid. The three-tube heater depicted in FIG. 2 is similar to FIG. 1, and the fuel conduit and oxidation conduit are the same. In FIG. 2, however, a process zone (15) is formed by process conduit (16). Process conduit (16), is a cylindrical pipe that has an inlet (32) for a process stream and an outlet (28) for a heated process stream. Alternately, the process stream may enter at (28) and exit the process conduit at (32) to provide a process flow co-current with the oxidation conduit flow.

FIG. 2 a is a cross-sectional view of FIG. 2 taken along line A-A. FIG. 2 a depicts an embodiment where the longitudinal axis of the opening intersects the longitudinal axis of the fuel conduit. Another embodiment, not shown, comprises an opening where the longitudinal axis of an opening is at a distance from the longitudinal axis of the fuel conduit such that the axes do not intersect.

FIG. 3 depicts a flameless combustion heater (100) that has a fuel conduit (102), an oxidation conduit (104), a process conduit (108), and an oxidant conduit (106). The fuel zone (111) is formed by fuel conduit (102) that is a cylindrical pipe or tube with angled openings (126) along the pipe. The oxidation zone (113) is formed by oxidation conduit (104) that is cylindrical and concentric to the fuel conduit. The process zone (117) is formed by process conduit (108), and it may be a cylindrical pipe or the shell side of a shell and tube heat exchanger. The oxidant zone (115) is formed by oxidant conduit (106) that is cylindrical and concentric to the oxidation conduit. During operation, the fuel enters the fuel conduit at inlet (110) and exits the fuel conduit at the angled openings (126). The angled openings (126) are angled in the direction away from the fuel inlet (110). The oxidant enters the oxidant conduit at oxidant inlet (114) and exits the oxidant conduit at oxidation conduit inlet (120). The oxidant is preheated in oxidant zone (115). The preheated oxidant is mixed with the fuel from openings (126) and the combustion products exit the heater at oxidation conduit outlet (112). A process stream may enter at (116) and exit at (118) or it may enter at (118) and exit at (116).

This embodiment is different from that shown in FIGS. 1 and 2 in some respects. The oxidant is preheated inside the heater because it is introduced into the oxidant conduit that is in a heat exchange relationship with the oxidation conduit and the process conduit. The oxidant may also be preheated before being introduced into the oxidant conduit. The process conduit is in heat exchange relationship with a portion of the oxidant and oxidation conduit. These different embodiments provide for more freedom to design the heater application to meet the requirements of the process and incorporate design features to recover additional heat from the combustion products of the flameless combustion.

FIG. 3 a is a cross-sectional view of FIG. 3 taken along line A-A. This figure depicts one embodiment where the longitudinal axis of an opening intersects the longitudinal axis of the fuel conduit. Another embodiment, not shown, comprises an opening where the longitudinal axis of an opening is at a distance from the longitudinal axis of the fuel conduit such that the axes do not intersect.

FIGS. 4-6 depict embodiments of flameless combustion heaters with what is hereinafter referred to as obtuse angled openings. FIG. 4 depicts a flameless combustion heater (10) that is similar to the two-tube flameless combustion heater depicted in FIG. 1, although the openings are angled in a different direction. The angled openings (20) are angled in the direction towards the fuel conduit inlet.

The openings are such that the longitudinal axis of an opening forms an angle of greater than ninety degrees with the inner surface of the oxidation conduit as measured from the inlet end of the fuel conduit. These openings are hereinafter referred to as obtuse angled openings. The longitudinal axis of an opening preferably forms an angle of from 100° to 160° with the inner surface of the oxidation conduit, more preferably from 105° to 145° and most preferably from 110° to 130°.

The longitudinal axis of an opening may intersect the longitudinal axis of the fuel conduit as depicted in FIG. 4 a. In the alternative, the longitudinal axis of an opening may be at a distance (40) from the longitudinal axis of the fuel conduit such that the axes do not intersect, as depicted in FIG. 4 b, and such openings are hereinafter referred to as obtuse angled tangential openings. Obtuse angled tangential openings provide for similar benefits as acute angled tangential openings.

Obtuse angled openings typically result in increased turbulence of the fuel flow and mixing with the oxidant in the oxidation conduit that improves the flameless combustion reaction. In addition, obtuse angled openings provide many of the same benefits that acute angled openings provide, for example, allowing the distance between the fuel conduit and the oxidation conduit to be reduced resulting in a smaller heater and reduced capital expenditure.

FIG. 5 depicts a flameless combustion heater (10) that is similar to the three-tube flameless combustion heater depicted in FIG. 2. FIG. 5 however depicts obtuse angled openings in the heater as described above. FIG. 5 a is a cross-sectional view of FIG. 5 taken along line A-A.

FIG. 6 depicts a flameless combustion heater (100) that is similar to the four-tube flameless combustion heater depicted in FIG. 3. FIG. 6 however depicts obtuse angled openings in the heater. FIG. 6 a is a cross-sectional view of FIG. 6 taken along line A-A.

FIGS. 7-9 depict embodiments of flameless combustion heaters with what is hereinafter referred to as tangential openings. FIG. 7 depicts a flameless combustion heater (10) that is similar to the two-tube flameless combustion heater depicted in FIG. 1, although the openings are angled differently. The tangential openings 20 are not angled in the direction of the fuel conduit inlet or outlet. FIG. 7 a is a cross-sectional view of FIG. 7 taken along line A-A.

The tangential openings are such that the longitudinal axis of an opening is at a distance (40) from the longitudinal axis of the fuel conduit such that the axes do not intersect. The distance between the longitudinal axis of the opening and the longitudinal axis of the fuel conduit may be greater than one-fourth of the internal radius of the fuel conduit, preferably greater than one-half of the internal radius of the fuel conduit and more preferably greater than three-fourths of the internal radius of the fuel conduit.

Tangential openings provide for more even heat release in the radial direction, similarly to acute and obtuse angled tangential openings.

FIG. 8 depicts a flameless combustion heater (10) that is similar to the three-tube flameless combustion heater depicted in FIG. 2. FIG. 8 however depicts tangential openings in the heater as described above. FIG. 8 a is a cross-sectional view of FIG. 8 taken along line A-A.

FIG. 9 depicts a flameless combustion heater (100) that is similar to the four-tube flameless combustion heater depicted in FIG. 3. FIG. 9 however depicts tangential openings in the heater. FIG. 9 a is a cross-sectional view of FIG. 9 taken along line A-A.

The flameless combustion heater may be operated at a variety of conditions depending on the particular configuration of heater and the heater application. Various examples and conditions are described in U.S. Pat. No. 5,255,742 and U.S. Pat. No. 7,025,940, which are herein incorporated by reference.

FIG. 10 depicts the use of a flameless combustion heater in an ethylbenzene dehydrogenation unit. A process feedstock containing steam and ethylbenzene is fed to the dehydrogenation reactor (204) via conduit (202). The dehydrogenation reactor (204) contains a suitable dehydrogenation catalyst, which may be an iron oxide based catalyst, and provides means for contacting the process feedstock with the dehydrogenation catalyst. A dehydrogenation reactor effluent is discharged from dehydrogenation reactor (204) through conduit (206) and introduced into the flameless combustion heater (208) through its process fluid inlet (210).

Because the dehydrogenation reaction is an endothermic reaction, the dehydrogenation reactor effluent will have a lower temperature than that of the process feedstock to the dehydrogenation reactor (204). The flameless combustion heater (208) is used to heat the dehydrogenation reactor effluent before it is introduced into the second stage dehydrogenation reactor (212). The heated process fluid passes from the flameless combustion heater (208) through its discharge outlet (214) and conduit (216) to be introduced as a feed into the second stage dehydrogenation reactor (212). A dehydrogenation reactor effluent is discharged from the second stage reactor (212) through conduit (218). The dehydrogenation process may be carried out with more than two reactors in which case a flameless combustion heater may be placed in front of each additional reactor.

Fuel is introduced to the flameless combustion heater (208) through conduit (220) and through fuel inlet (222). Oxidant is introduced into the heater (208) through conduit (224) and through oxidant inlet (226). The combustion products are discharged from the flameless combustion heater (208) through conduit (228).

A preheater (230) is shown in this embodiment to preheat the oxidant before it is passed into the heater (208). This is an optional part of the heater system.

The flameless combustion heater described herein can be used in any application with any variation of the described details of opening location and geometry. 

1. A flameless combustion heater comprising an oxidation conduit and a fuel conduit having a plurality of openings that provide fluid communication from within the fuel conduit to the oxidation conduit wherein the longitudinal axis of at least one opening forms an oblique angle with the inner surface of the oxidation conduit.
 2. A heater as claimed in claim 1 wherein the longitudinal axis of the at least one opening forms an acute angle with the inner surface of the oxidation conduit, as measured from the inlet end of the fuel conduit.
 3. A heater as claimed in claim 2 wherein the angle is less than about 80 degrees.
 4. A heater as claimed in claim 2 wherein the angle is greater than about 20 degrees.
 5. A heater as claimed in claim 2 wherein the angle is from about 35 to about 75 degrees.
 6. A heater as claimed in claim 2 wherein the angle is from about 50 to about 70 degrees.
 7. A heater as claimed in claim 1 wherein the longitudinal axis of the at least one opening forms an obtuse angle with the inner surface of the oxidation conduit, as measured from the inlet end of the fuel conduit.
 8. A heater as claimed in claim 7 wherein the angle is greater than about 100 degrees.
 9. A heater as claimed in claim 7 wherein the angle is less than about 160 degrees.
 10. A heater as claimed in claim 7 wherein the angle is from about 105 to about 145 degrees.
 11. A heater as claimed in claim 7 wherein the angle is from about 110 to about 130 degrees.
 12. A heater as claimed in claim 1 wherein a majority of the openings form oblique angles with the inner surface of the oxidation conduit.
 13. A heater as claimed in claim 1 wherein all of the openings form oblique angles with the inner surface of the oxidation conduit.
 14. A heater as claimed in claim 1 wherein the longitudinal axis of the at least one opening does not intersect the longitudinal axis of the fuel conduit.
 15. A heater as claimed in claim 14 wherein the distance between the longitudinal axis of the opening and the longitudinal axis of the fuel conduit is greater than one-fourth of the internal radius of the fuel conduit.
 16. A heater as claimed in claim 14 wherein the distance between the longitudinal axis of the opening and the longitudinal axis of the fuel conduit is greater than one-half of the internal radius of the fuel conduit.
 17. A heater as claimed in claim 1 wherein the longitudinal axis of one opening forms a first angle with the inner surface of the oxidation conduit and the longitudinal axis of another opening forms a second angle with the inner surface of the oxidation conduit that is not equal to the first angle.
 18. A heater as claimed in claim 1 wherein at least one opening has a circular cross-section.
 19. A heater as claimed in claim 1 wherein one opening has a cross-sectional area that is greater than the cross-sectional area of another opening.
 20. A heater as claimed in claim 1 further comprising an oxidant conduit, the oxidant conduit having an inlet for oxidant and an outlet for preheated oxidant that is in fluid communication with the inlet of the oxidation conduit.
 21. A heater as claimed in claim 1 further comprising a process conduit in a heat exchange relationship with the oxidation conduit.
 22. A heater as claimed in claim 21 wherein the process conduit is adapted for carrying out an endothermic chemical reaction.
 23. A heater as claimed in claim 1 further comprising a preheater in fluid communication with the flameless combustion heater, wherein the preheater is capable of preheating the oxidant to a temperature at which when the oxidant and fuel are mixed in the oxidation conduit, the temperature of the mixture exceeds the auto-ignition temperature of the mixture.
 24. A heater as claimed in claim 21 wherein the oxidant conduit is in heat exchange relationship with the process conduit.
 25. A heater as claimed in claim 1 wherein the heater further comprises an oxidation catalyst.
 26. A heater as claimed in claim 25 wherein the oxidation catalyst is selected from the group consisting of palladium, platinum and mixtures thereof.
 27. A method for providing heat to a process conduit comprising: providing an oxidation conduit; providing a fuel conduit having a plurality of openings that provide fluid communication from within the fuel conduit to the oxidation conduit wherein the longitudinal axis of at least one opening forms an oblique angle with the inner surface of the oxidation conduit; providing a process conduit in a heat exchange relationship with the oxidation conduit; introducing fuel into the fuel conduit; introducing an oxidant into the oxidation conduit; and introducing the fuel into the oxidation conduit through the plurality of openings such that flameless combustion occurs in the oxidation conduit. 